1. Field of the Invention
This invention generally relates to an interface apparatus in a computer system. More particularly, the present invention relates to a general purpose data input/output interface system through a removable magnetic storage unit.
2. Description of the Prior Art
Conventional computer data I/O interface systems have employed a serial or parallel bus connection through which the data is sent in either serial or parallel form to an external device. Over the years, various standards have evolved like the RS232 for the serial port and the Centronics printer interface for the parallel port. The popularity of these standard ports resulted in their inclusion in most of the computers manufactured today. These ports are being used to interface the computer to a large variety of devices, including printers and plotters, modems and other communication systems, control systems, instruments, device programmers, dataloggers, desktop computer to laptop computer communication and more.
One of the disadvantages of both the serial and the parallel ports is their relative low speed. A typical serial port device can work up to 64K baud, while a typical parallel port has a bandwidth of up to 100 Kbit/Second. Another related disadvantage is that since both ports do not employ a DMA (Direct Memory Access) mode of operation, they require full CPU attention during transfer of data.
Many applications need to be interfaced to the computer for only a relatively short period of time during an occasional file transfer. Since it is not possible to replace the current device which is connected to the port while the computer is still on, the ports have serious disadvantages for such short time applications. Also, as the ports are usually located at the rear of the computer, they have a limited access which make them even more unsuitable for frequent replacement of applications.
In addition to the standard serial and parallel ports, other application specific data I/O interface boards have been developed. Such interface boards are typically plugged in an expansion slot in the computer main board. While these boards provide the specific speed requirements of their applications, they are relatively costly, and they are also not useful for frequently replaced applications for the same reasons that limit the standard ports. Yet another disadvantage of such interface boards is the fact that any computer has a limited number of expansion slots into which such boards can be connected. With continuous development of applications that may be interfaced to the computer, the issue of available expansion slots becomes critical.
As the serial and parallel ports, as well as the application specific data I/O interface boards, are directly wired to the external application, any hazardous electrostatic charges or noise which is either attacking the external application or generated within it, will in turn propagate through the connection wiring directly into the computer circuitry and may cause significant damage. This is clearly another problem associated with the prior art.